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<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <canvas id="tutorial" width="300" height="300">
    <img src="https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1601203384027&di=5e247bed086d035d9b5f41aec350c1d8&imgtype=0&src=http%3A%2F%2Fimg.ui.cn%2Fdata%2Ffile%2F0%2F8%2F9%2F2251980.png" alt="11">
  </canvas>
  <script type="text/javascript">
  function draw(){
      var canvas = document.getElementById('tutorial');
      if(!canvas.getContext) return;
        var ctx = canvas.getContext("2d");
        //开始代码
      
  }
  draw();
  </script>
  </body>
</html>